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When an analyst at NFL.com this week put out his list of the NFL’s top rookies at the Week 6 point of this season, the 49ers’ Eric Reid was on it.

Reid, the former LSU standout safety, was No. 7 on analyst Chris Wesseling’s group, with Wesseling noting, “It’s not hyperbole to suggest that Reid is a playmaking upgrade on Dashon Goldson. … The first-rounder’s range jumps off the screen.”

But over the past few weeks, another rookie defender has been making a big impact, too: outside linebacker Corey Lemonier. And as the season progresses, it seems more and more likely that Lemonier could make his way on to quite a few “best rookies” lists by the end of the year.

Lemonier, from Auburn, has been splitting time with veteran Dan Skuta at right outside linebacker, the position vacated by All-Pro Aldon Smith, who currently is away from the team in a treatment program. It’s possible that Smith, who also is dealing with some off-the-field legal issues, may not return this season.

According to Eric Branch of the San Francisco Chronicle, Lemonier has played 121 snaps, with Skuta getting 95, since Smith left the team.

The 49ers drafted Lemonier for his pass-rushing abilities, and he’s been playing in passing downs in the nickel defense, with Skuta getting the majority of snaps in the base defense.

This past Sunday, Lemonier came up with his first NFL sack, and it was a big one. Early in the victory over the Arizona Cardinals, he brought down quarterback Carson Palmer in the end zone for a safety. Lemonier also forced a fumble that was recovered by the 49ers, batted down a pass and had another hit on Palmer.

Though the sack was his first, Lemonier has been providing pressure. As Branch noted, in 78 rushes this season, Lemonier has eight quarterback hurries and two QB hits.

Lemonier has been excited to get more playing time than he expected this season. But when the 49ers selected him in the third round (No. 88 overall pick), they believed he had the potential to be a strong NFL pass rusher. Like Smith, Lemonier is making the switch from college defensive end to outside linebacker in a 3-4 defense.

Bill Williamson of ESPN.com, who covers the 49ers, wrote recently that Scouts, Inc., draft expert Steve Muench believes there are questions about how well Lemonier – pronounced Lemon-yay – can play against the run, but his pass-rush abilities are solid.

“His initial burst and closing speed make him a constant threat rushing off the edge,” wrote Muench. “For what it’s worth, he posted the third-fastest 40-yard time and 10-yard split at the 2013 combine. He also has the length, upper-body strength and lateral mobility to develop a variety of pass-rush moves.”

At Auburn, Lemonier was known for the time he spent in the weight room and the effort he put forth on the practice field. One of his coaches at Auburn told the San Francisco Chronicle this year that, “His work habits really outshone his ability, and he never stopped working to get better.”

Now, Lemonier is doing the same thing as a first-year pro, working hard every week to get better. He’s been a big part of the 49ers’ three-game winning streak, and he’ll get a chance for his second sack this Sunday when San Francisco (4-2) takes on the host Titans (3-3) in Tennessee Sunday.

“He is coming along well,” 49ers safety Donte Whitner told the team’s website after the win over the Cardinals. “From the first day he came in, I could see he is an intelligent guy that wants to work hard. That’s why he’s able to make the plays he made today. He has all the mechanics, all the makeup, he has all the talent to be a good pass-rusher in the National Football League. He just has to get more experience and he’ll get better and better.”